Inoculating alloys consisting of si-al-ca-ba-mn-zr-fe



United States Patent 3,272,623 INOCULATING ALLOYS CONSISTING 0FSi-Al-Ca-Ba-Mn-Zr-Fe Walter Crafts, Niagara Falls, N.Y., and Peter F.Wieser,

Cleveland, Ohio, assignors to Union Carbide Corporation, a corporationof New York No Drawing. Filed Oct. 28, 1963, Ser. No. 319,505 8 Claims.(Cl. 75134) The present invention relates to addition alloys for use inthe manufacture of cast iron. More particularly, the present inventionrelates to addition alloys for reducing chill depth in iron castingswhich addition alloys can be.

used Without the formation of interfering amounts of slag or dross.

The inoculation of cast iron with alloy additions for the purpose ofavoiding the formation of iron carbide during solidification has beenpracticed for many years. The intent in using alloy additions is tominimize the hard chilled surface in rapidly cooled parts of castingsand to minimize the formation of undesirable undercooled microstructuresof fine graphite and associated soft ferrite, to thus provide uniformityof hardness, higher strength, and improved wear resistance in the castiron.

Various alloy addition agents have been used as inoculants in attemptsto achieve the aforementioned benefits, and it is recognized thateffective inoculation is a nucleating mechanism that produces a changein microstructure and properties in cast iron that aredisproportionately large in relation to the change made in the chemicalcomposition of the cast iron. One family of commonly used inoculants isbased on ferrosilicon in combination with other alloying elements.Silicon itself has a softening effect on the cast iron, whether it isadded during melting or pust prior to solidification. This effect ofsilicon generally is considered to result from an alloying effect thatis more or less proportional to the amount present in the cast iron andnot to result from the nucleating effect of an inoculant. This relationis described in the Metals Handbook, 8th Edition, pp. 349-365 and379-394, American Society for Metals, 1961.

Silicon alloys containing various other elements to improve theinoculation of cast iron have been used for many years as noted in theabove-mentioned articles.

However, it has been found that with the presently known additionagents, the use of alloy constituents which are generally consideredbeneficial as regards inoculation, cause various undesirable effects inuse which substantially offset any advantages obtained. For example,presently known inoculating agents in the form of ferrosilicon alloyedwith other elements have low rates of dissolution and also tend toproduce increased amounts of slag or dross when the constituents of theinoculating agent are oxidized, very often with the retention of slag inthe solidified castings which causes surface defects and porosity.

It has been discovered, however, as part of the present invention, thatby closely controlling the constituents in addition agents, it ispossible to achieve highly effective inoculation while avoiding theaforementioned difficulties associated with the formation of slag anddross.

Accordingly, it is an object of this invention to provide an alloyaddition agent which will effectively inoculate molten iron to produce acast iron of reduced chill depth with uniform structure and properties.

It is another object to provide an alloy addition agent which willdissolve rapidly in molten iron.

A further object is to provide an alloy addition agent which willdissolve in molten iron without excessive formation o-f slag, such slagas is formed being refractory and readily removable from the surface ofthe iron bath prior to casting.

"ice

Other objects will be apparent from the following description andclaims.

An addition agent in accordance with the present invention is an alloyof silicon, aluminum, calcium, and barium, manganese and zirconium.

It has been discovered, as part of the present invention, that byincluding all of the foregoing elements in the composition of an alloyaddition agent, and by closely controlling the amounts of the respectiveelements, undesirable dross and slag conditions can be avoided While atthe same time substantially improved chill reduction is provided.

In order to achieve the full benefits of the invention, the compositionof the alloy addition agent in weight percent must be within the rangeSilicon 35-85 Aluminum 0.5-1.5

Calcium 0.5-4.0

Barium I- 0.5-4.0

Manganese 2-7 Zirconium 2-7 Iron Balance A preferred range for the alloyaddition agent of the present invention is:

Silicon 60-65 Aluminum .75-1.25 Calcium 1-2.5

Barium 2-3 Manganese 5-7 Zirconium 5-7 Iron Balance A particularlyeffective range for providing a very high chill reduction whilepractically eliminating the slag and dross problem is:

Silicon 61-66 Aluminum 0.5-1

Calcium 1-2.5

Barium 1-2 Manganese 4-6 Zirconium 2-3 Iron Balance In order toillustrate the effect of various alloy additions, a system of evaluatingreduction in chill depth in cast irons and other properties wasdeveloped and used in the testing of various specimens.

In the testing two common types of base irons were employed. One havingan average carbon equivalent (CE=C /s(Si+P)) of 4% and characterized asa soft iron (C=3.3%, Si=2%, Mn=0.8%, S:0.12%) and a second having anaverage carbon equivalent of 3.5% characterized as a hard iron (C=2.9%,Si=l.6%, Mn=0.7%, S=0.l%).

Both types of iron were used in the preparation of test specimens andwere prepared by melting a charge of pig and Armco iron with minoradditions of other elements as required to produce the desiredcomposition, in an induction furnace with a basic lining, forming a heatof about pounds weight. More particularly, in preparing the specimens,the primary charge of a major portion of the pig iron and all of theArmco iron were placed in the furnace, heated, and when substantiallymelted, the remaining pig iron and minor elements were added. The bathwas deoxidized with silicon, deslagged, and the remainder of therequired silicon added. Any remaining slag was removed, and thetemperature was adjusted to 1500 C. The power input to the furnace wassuch as to maintain the bath at about 1500 C. (measured by immersionthermocouple) throughout the subsequent tapping operations.

A weighed quantity of the molten iron was tapped into a clay-linedgraphite ladle, which had been preheated to a red heat in a gas-firedfurnace. An inoculating alloy was added to the tapped molten iron, andthe metal was stirred with a steel rod. When the temperature dropped towithin the range of 1320 to 1350 C., the molten metal was cast into testspecimens which were a standard 1.2-inch diameter by 21-inch longarbitration bar, and an ASTM Type 40 chill test bar.

Additional taps of molten metal were separately treated with differentinoculants and cast in the same manner, to provide additional testspecimens. Also, additional taps were processed in the same manner butnot treated with any inoculant and thus served as a standard forsubsequent comparative measurements. The amount by weight of additionalloy added in each instance was controlled to provide an addition of0.1 to 0.3 percent silicon to the cast iron. For twenty pound taps, theamount of addition alloy was on the average, about 0.06 lb.

Specimens of soft and hard irons prepared in the foregoing manner weretested and observed as regards chill depth, rate of solution anddross-forming behavior. The chill depth, i.e. the white iron structureproduced in the castings as a result of rapid solidification, wasmeasured in accordance with standard practice.

In rating the effectiveness of the inoculants in con- 4 Slower than 3and questionable whether complete solution is reached after one minute.

5 Incomplete solution after one minute or more.

Dross-forming characteristics Scale A Virtually no dross, as in the caseof ferrosilicon pure enough to have practically no inoculating effect.

Light dross that may require skimming but does not usually result indefective castings.

C Dross that usually requires skimming to avoid defective castings.

Heavy dross that requires extensive and continued skimming; soundcastings are produced with difficulty.

Refractoriness of dross Scale S Stiff and coagulating, covering lessthan of metal surface. L Liquid, covering less than 25% of metalsurface. V Viscous-fluid, covering virtually 100% of metal surface.

The following Table I sets forth data obtained in the preparing andtesting of cast specimens in the manner hereinbefore described and alsodata obtained as a result of field tests.

TABLE I Additional Alloy Percent Si added Percent Chill Reduction toCast Iron Rate Test Percent Percent Percent Percent of Dross Specimen BaMn Zr Fe Sol.

Percent Percent Percent Soft Hard Soft Iron Hard Iron Si A1 21 Iron Iron63 1 3. 5 2. 5 6 6 Bal. 15 3 100 96 3 CS 66 0.62 2.13 1.55 5. 6 3 Ba].0. 2 98 3 BS 63 0.5 1. 10 1. 23 4 2.28 Bal. 0.2 98 2-3 BS 63 1 3. 5 0.23 CV 66 0.9 5.2 0.2 4 CV 1. 5 10 0.15 5 DS 65 1. 5 15 0.15 5 DV l 2. 50.15 3 DS 75 1 2.5 0. 15 3 CS 75 0.4 0.5 0.2 1 AL trolling chill depth,the following formula was used:

Percent Reduction in Chill Depth= Chill depth of base iron-chill depthof inoculated iron X100 chill depth of base iron The solution rate anddross-forming characteristics of the various addition alloys tested werealso evaluated using the following standards:

Rate of solution about one minute.

As can be seen from the data of Table I, the first three additionalagents, which are in accordance with the present invention, provide themost desirable combinations of properties. For example, the chillreduction is greater than in each case, the solution times are 1 minuteor less, and the dross is essentially non-interferring.

On the other hand, the other addition agents shown in the table, whichare not in accordance with the present invention provide a combinationof lesser chill reduction and generally undesirable dross formation andsolution times.

It is to be particularly noted that Tests XIII, XIV, XV, XVI, and XVIIshown in Table I illustrate the criticality of the compositional rangesof the present invention by showing that alloy addition agents which areeffective in reducing chill depth do not necessarily have suitablesolution times or dross forming characteristics.

In addition to the aforedescribed tests, various comparative field testswere conducted using the addition agents listed below.

FIELD TEST ADDITION AGENTS As can be seen addition agents A and B are inaccordance with the present invention While addition agents C, D and Eare not.

In the first of the field tests the addition agents B, D and E wereseparately used in the amount of about five pounds per 2500 pounds ofcupola iron. The additions were made during tapping of the iron intoidentical foundry ladles. Motion pictures were taken of the drossfloating on the surface of the iron in order to obtain a comparison ofthe type and quantity of the dross resulting from the various additions.

In the use of addition agent 13 of this invention the results weresubstantially the same as for Test Specimen 42/ SZ5 1 as noted in TableI. The average coverage of the metal surface was 18% using additionagent B and the dross was dry or easily skimmed.

Addition agents D and E each resulted in a DV type dross and the averagemetal coverage for each was about 80%.

In a further field test, using addition agents A and C, five pounds ofaddition alloy Were added per ton of cupola iron. The use of additionagent A resulted in a relatively small amount of dry dross and about a19% improvement in chill reduction as compared to the results obtainedusing addition agent C.

In another test, adding two pounds of addition alloy per 800 pounds ofcupola iron, addition agent A prov-ided about a 37% improvement in chillreduction as compared to the results obtained using addition agent C.

In still another test, about 1.5 pounds of addition alloy were added inthe ladle to 900 pounds of cast iron, the treated iron being held in theladle for about 8 minutes before pouring. The chill depth in castingsfrom the metal treated with addition agent A was 7 mm. as compared to 12mm. for the same castings from metal treated With addition agent C.

In all of the foregoing field tests, the dross resulting from the use ofaddition agent A was substantially drier and in substantially smalleramounts as compared to the dross resulting from the use of additionagent C.

What is claimed is:

1. An addition alloy for use in the manufacture of cast iron consistingessentially of about 35 to about 85% silicon, about 0.5 to about 1.5%aluminum, about 0.5 to about 4% calcium, about 0.5 to about 4% barium,about 2 to about 7% manganese, about 2 to about 7% zirconium, balanceiron.

2. An addition alloy for use in the manufacture of cast iron consistingessentially of about to about silicon, about 0.75 to about 1.25%aluminum, about 1 to about 2.5% calcium, about 2 to about 3% barium,about 5 to about 7% manganese, about 5 to about 7% zirconium, balanceiron.

3. An addition alloy for use in the manufacture of cast iron consistingessentially of about 63 to about 66% silicon, about 0.5% to about 1%aluminum, about 1 to about 2.5% calcium, about 1 to about 2% barium,about 4 to about 6% manganese, about 2 to about 3% zirconium, balanceiron.

4. An addition alloy for use in the manufacture of cast iron consistingessentially of about 63% silicon, about 1% aluminum, about 3.5% calcium,about 2.5 barium, about 6% manganese, about 6% zirconium, balance iron.

5. An addition alloy for use in the manufacture of cast iron consistingessentially of about 66% silicon, about 0.6% aluminum, about 2.1%calcium, about 1.6% barium, about 5.6% manganese, about 3% zirconium,balance iron.

6. An addition alloy for use in the manufacture of cast iron consistingessentially of about 63% silicon, about 0.5% aluminum, about 1.1%calcium, about 1.2% barium, about 4% manganese, about 2% zirconium,balance iron.

7. An addition alloy for use in the manufacture of cast iron consistingessentially of about 65% silicon, about 0.8% aluminum, about 1.5%calcium, about 2.8% barium, about 6.3% manganese, about 5.3% zirconium,balance iron.

8. An addition alloy for use in the manufacture of cast iron consistingessentially of about 61% silicon, about 0.6% aluminum, about 2.1%calcium, about 1.6% barium, about 5.7% manganese, about 2.8% zirconium,balance iron.

References Cited by the Examiner UNITED STATES PATENTS 2,767,084 10/1956Chandler -134 2,810,639 10/1957 Kessler 75134 X 2,950,187 8/1960 Ototani75---124 X 3,137,570 6/1964 Mickelson 75--124 3,215,525 11/1965 Sprankle75134 HYLAND BIZOT, Primary Examiner.

R. O. DEAN, Assistant Examiner.

1. AN ADDITION ALLOY FOR USE IN THE MANUFACTURE OF CAST IRON CONSISTINGESSENTIALLY OF ABOUT 35 TO ABOUT 85% SILICON, ABOUT 0.5 TO ABOUT 1.5%ALUMINUM, ABOUT 0.5 TO ABOUT 4% CALCIUM, ABOUT 0.5 TO ABOUT 4% BARIUM,ABOUT 2 TO ABOUT 7% MANGANESE, ABOUT 2 TO ABOUT 7% ZIRCONIUM, BALANCEIRON.